@essexboy
I still owe you an answer:
Since the issue was showing only during the first boot of the day the search for the cause was a bit time consuming, just one try per day!
It was all waisted time because 2 day ago my system started on the first boot of the day in the normal 25-30 seconds in the configuration which I started out with. And it still does today.
May be this obscure EM-Update everybody is talking about has something to do with it.
But I tell you what: I don’t have any clue.
Sorry when I disappoint you with this “Solution”. At least I’m happy to have the normal behaviour again! 8)